Mantle discontinuity structure beneath China

Mantle reflectivity profiles obtained from long-period recordings of multiple-ScS reverberations from intermediate and deep-focus earthquakes surrounding China reveal remarkably sharp images of China deep structure. Regional inversion of the reflection coefficient of the 410-km discontinuity, R(410), reveals a pronounced high beneath Mongolia and north to northwestern China which is best explained by increased upper mantle olivine content, signifying extensive basalt depletion in a tectosphere that extends below the 410-km discontinuity. A low value of R(660) associated with topographic depression of the 660-km discontinuity beneath eastern Asia is consistent with a horizontally inclined slab atop the phase transition marking the seismic discontinuity. Two lower mantle reflectors (one beneath southern Honshu, Kyushu, and the Sea of Japan; the other below Shantung province (China) and the Yellow Sea) correlate with horizontally elongated velocity anomalies in western Pacific seismic tomography models. -from Authors